Exhibit 5.1

May 22, 2015

IDEXX Laboratories, Inc.

One IDEXX Drive

Westbrook, Maine 04092

Ladies and Gentlemen:

Reference is made to the above-captioned Registration Statement on Form S-8 (the “Registration Statement”) to be filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), relating to an aggregate of 700,000 shares of common stock, $.10 par value per share (the “Shares”), of IDEXX Laboratories, Inc., a Delaware corporation (the “Company”), issuable under the IDEXX Laboratories, Inc. 1997 Employee Stock Purchase Plan, as amended (the “Plan”).

In rendering the opinion expressed below, we have examined the Plan, the Restated Certificate of Incorporation and the Amended and Restated By-Laws of the Company, each as amended and restated to date, and originals, or copies certified to our satisfaction, of all pertinent records of the meetings of the directors and stockholders of the Company, the Registration Statement and such other documents relating to the Company as we have deemed appropriate. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

In our examination of the foregoing documents, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as certified, photostatic or other copies, the authenticity of the originals of any such documents and the legal competence of all signatories to such documents.

For purposes of the opinion expressed below, we have assumed that a sufficient number of authorized but unissued shares of the Company’s common stock will be available for issuance when the Shares are issued. We have also assumed that the appropriate action has been or will be taken, prior to the offer and sale of the Shares in accordance with the Plan, to register and qualify the Shares for sale under all applicable state securities or “blue sky” laws to the extent required.

We express no opinion herein as to the laws of any state or jurisdiction other than the General Corporation Law of the State of Delaware and the federal laws of the United States of America.

It is understood that this opinion is to be used only in connection with the offer and sale of the Shares while the Registration Statement is in effect.

Please note that we are opining only as to the matters expressly set forth herein, and no opinion should be inferred as to any other matters.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized for issuance and, when the Shares are issued and paid for in accordance with the terms and conditions of the Plan, the Shares will be validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration Statement and further consent to the use of our name wherever appearing in the Registration Statement and any subsequent amendments. In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission. This opinion speaks only as of the date hereof and we assume no obligation to update this opinion at any date subsequent to the date hereof.